My colleague on the ModTeam and good friend Dwayne/dewey2k has a great answer for you: "Labels are for cans." What he means by that is who cares whether you are straight or gay or bi. The important thing is to be true to yourself.
My own strategy on this is to say this: Ask yourself three questions about your sexuality:
1. Are you being honest wth yourself about your feelings and sexual desires?
2. Are you being honest and responsible with your partners?
3. Do you feel sexually fulfilled?
If you can genuinely say that the answer to all those questions is "yes", then hey, you're in good shape and it doesn't matter where you happen to be on the spectrum from straight to bi to gay. Most people are not entirely straight or entirely gay anyway, but have feelings, curiosities, and urges that place them somewhere in between.
Nobody living can ever stop me
As I go walking my freedom highway.
Nobody living can make me turn back:
This land was made for you and me. (Woody Guthrie)